Induction heating is used to heat treat metal parts such as steel bars, slugs, billets, bar ends, tubes, slabs and the like by passing the metals through a pathway heated by an induction coil. A typical induction heating apparatus can have one coil being contained within a single refractory housing or more coils, aligned linearly, in separate housings. The metal parts are passed through the pathway and heated by the aligned induction coils.
Typical induction heating processes are carried out in an oxygen-containing environment such as air. The presence of oxygen, however, results in the formation of scale on the heated metal parts. Scale is an abrasive which significantly contributes to the wearing of the forging dies, reducing their useful life. Scale builds up within the housing thereby reducing the useful life of the induction coils.
There have been efforts to introduce an inert gas into the pathway of the induction heating apparatus to eliminate or at least substantially reduce the presence of oxygen. In those operations where the induction coils are contained in separate housings, a cover has been placed over the space between the housings to provide an air-tight enclosure. Multiple inlets have been provided in the cover to transport an inert gas from a source into the pathway contained within the cover. The inert gas then diffuses into the housing to provide a more acceptable gaseous environment for conducting induction heating and subsequent forging.
Such methods, however, suffer from a number of disadvantages. First, the covers are of unitary construction and are permanently affixed to the housing. When visiting the inductor, the cover must be destroyed to provide access to the pathway within the housing. Only after the cover is removed may the housing be visited for maintenance. Once the maintenance operation is complete, a new cover must be placed over the spaces between the housings. As is apparent, the destruction of the original cover and replacement with a new cover is time consuming and adds significantly to the cost of induction heating.
Another disadvantage of prior attempts at induction heating in an inert atmosphere involves the lack of control of the injection of the inert gas and the inability to provide a barrier against the infiltration of unwanted gases such as air due to drafting. More specifically, induction heating devices never achieve complete protection against air leaks. For example, it is known that air enters the induction heating apparatus through (a) the entryway where the cold metal parts enter the apparatus and (b) the exit where the heated parts leave the apparatus. In addition, air leaks may be present where the cover is attached to the housing of the induction heating apparatus. The infiltration of air into the heating areas produces scaling.
It would be of significant benefit in the art of induction heating to minimize scaling and to eliminate the need to replace the covers to provide access to the induction coil apparatus for maintenance. It would be of further benefit to provide greater control over the introduction of an inert gas into the induction heating apparatus.